Battery Storage FAQs

What are the different types of battery?

Lead Acid Batteries: Lead acid batteries are the most common type of energy storage.

All lead acid batteries are based on the same lead/sulphuric acid chemical reaction, however, they have evolved into different types – each designed for a specific need.

Smaller batteries look like big car batteries and contain several cells in tough plastic cases to give 6V or 12V with capacities up to ~ 200Ah. They are either flooded cell types: with a vent for gassing and topping-up with distilled water; or sealed/ gel types: with an immobilised electrolyte.

Larger battery banks are usually made up of flooded 2V cells ranging in capacity of ~100Ah to several thousand. Sealed types are also available. Some flooded cell batteries using tubular positive plates instead of flat plates have longer life.

Lithium Ion Batteries:

These have several advantages over conventional lead acid batteries:

  • Higher energy density: more energy with less size or weight
  • Higher charge & discharge currents possible so shorter charging times and bigger loads possible.
  • Longer battery life (up to six times)
  • Higher efficiency between discharging & charging.
  • Higher continuous power available.

Nickel Cadmium Batteries:

These are manufactured in many sizes. Sealed ones have very small capacities but are useful for self contained lights.

The larger ‘wet’ nicad is ideal for wind/solar energy storage. They require little maintenance; can be 100% discharged; left in any state of charge without damage; withstand overcharging; and withstand temperature extremes. However, they are several times the price of lead acid batteries. There are issues concerned with storage & recycling due to the toxic nature of Cadmium.

Why is battery capacity important?

If discharged at a higher rate (by a higher current) then battery capacity is reduced considerably. The maximum charge/discharge current should be less than 10% of battery Ah capacity.

  • Lower temperatures significantly reduce battery capacity (figures are at 25 deg C).
  • The older a battery becomes, the lower will be the capacity that can be obtained from it.

The capacity of the battery bank needed depends upon:

  • amount of storage required
  • types of charging source
  • maximum charge & discharge rates
  • temperature of operation.

The one requiring largest capacity will dictate battery size.

What is the typical lifetime of a battery?

This is measured in number of discharge/charge cycles rather than years. The more deeply the battery is discharged the lower the number of cycles it will last for. The percentage depth of discharge (DOD) of a battery means how much of the available power in the battery is used before recharge.

What are the rules regulating the installation of a battery?

Overcharging a battery raises the temperature of the electrolyte, causing excessive gassing, loss of distilled water and eventually damage to the plates.  Excessive discharge of a battery can also lead to permanent damage. If a battery is close to its fully discharged state it should be recharged immediately (eg. by using a generator & charger) – or if that is not possible all loads switched off until the battery can be charged.

Why do batteries need equalisation, and what does that mean?

Batteries need to be regularly boost charged and allowed to ‘gas’ freely for an hour or so. This equalises individual cell voltages within the battery and helps avoid electrolyte stratification.

How efficient are batteries at storing energy?

No battery is 100% efficient. Energy is lost in storage, charging and discharging. With new cells, efficiencies of 90% can be expected, however this decreases with age, sulphation and stratification. To maximise efficiency, batteries should be kept at room temperature, and sized correctly for their purpose, both to minimise self discharge, and to prevent them being charged and discharged too rapidly.

What is the recommended care for the battery?

The battery bank should be installed, preferably on its own, in a weather & frost protected, well ventilated shed or other enclosed area. Ideal temperature is ~ 20 ºC and should not be more than 43 ºC.

  • For optimum performance, batteries should all be of the same brand, age and amp-hour capacity within a battery bank.
  • Proper battery connections should be used, designed for high currents & long life. Connections should be tight and covered with petroleum jelly to prevent corrosion.
  • Batteries produce explosive hydrogen gases during charging, so avoid sparks or flames. They contain corrosive chemicals.

What is the battery state of charge?

This is how much of the battery capacity is available (how full it is). The most convenient way of determining this is by measuring the battery voltage. Ideally for a battery that has been at rest for three hours (ie. neither being charged or discharged). Measurement should only be performed with an accurate hydrometer. The normal automotive type is not suitable. A hydrometer cannot be used with sealed or gel-cell batteries.

Contact us for more Battery Storage information


If you want any more information on battery storage, simply get in touch with our renewable energy experts. Call our team on 0118 984 1753, or leave your details on our contact us page and await a swift reply.

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